1. Field of the Invention
The present invention relates to a method of and an apparatus for automatically assembling components within a differential case, to manufacture a differential gear device or unit which provides a major portion of a differential assembly.
2. Discussion of the Related Art
A differential gear device used as a final reduction gear on a motor vehicle, for example, employs a housing structure known as a differential case. The differential case accommodates a pair of opposed differential side gears (having a relatively large diameter) rotatable about an axis, and a pair of differential pinions (having a relatively small diameter) which are interposed between the side gears and mesh with these side gears. The differential pinions are supported by a pinion shaft or pin rotatably thereon about an axis perpendicular to the axis of rotation of the side gears. Where the differential gear device is used for a motor vehicle, the differential case is provided with a ring gear (a speed reduction gear having a relatively large diameter) attached thereto, and is rotated with the ring gear, about the axis of the differential side gears, so that power from the drive shaft is distributed to the right and left drive wheels connected to the respective differential side gears.
For improving the efficiency in assembling a differential assembly as described above, an automatic assembling apparatus is proposed as disclosed in JP-A-63-200935, for example. Up to the present, however, automatic assembling of the components within the differential case to provide a differential gear device which constitutes a principal part of the differential assembly has been infeasible because of comparatively small or substantially no clearances between the components, and the necessity of inserting the components into the differential case through openings formed through the case. Thus, there has been a long-felt need of automating the assembling of the differential gear device.
Described in detail, the differential gear device is assembled by first fixing a differential case upright, and holding a pair of differential side gears at respective positions in the upper and lower portions of the interior chamber of the upright differential case, by using suitable jigs or fixtures. Then, a pair of differential pinions are introduced into the differential case, for meshing engagement with the side gears, with part-spherical washers being placed on the rear or outer end faces of the pinions. For inserting a pinion shaft so as to rotatably support the pinions, the meshing differential side gears and pinions are rotated relative to the differential case about the axis of rotation of the side gears, with the washers held in place on the differential pinions, so that the pinions are moved relative to the case, so as to be aligned with concentric pinion shaft holes formed through the wall of the differential case. Then, the pinion shaft is inserted through the pinion shaft holes, pinion gears and washers, from the outside of the differential case, and a lock pin is driven into the pinion shaft through the wall of the differential case, to lock the shaft to the case.
The above assembling procedure requires the two differential pinions to mesh with the differential side gears at respective positions which are symmetrical with each other with respect to the axis of rotation of the side gears in a plane perpendicular to that axis, namely, at diametrically opposite positions on a circle whose center lies on the axis of the side gears. Further, the part-spherical washers should be retained in place on the outer end faces of the pinions by adhesion with an oil applied therebetween, while and until the pinions are moved into alignment with the pinion shaft holes, with the washers sliding on the inner wall surface of the differential case. The washers tend to be displaced relative to the pinions, during movement of the pinions relative to the differential case, with a result of misalignment of the washers with respect to the pinion shaft holes. Consequently, the assembling procedure requires a considerable time and a high level of skill for inserting the pinion shaft through the case, pinions and washers, in particular. According to a conventional manual assembling procedure, an experienced worker generally requires as long as approximately one minute for completing the assembling of one differential gear device, for instance.